Field of the Invention
Embodiments of the current invention relate to ceramic substrates in general and to a conductive layer on an upper surface of a ceramic substrate in particular.
Description of the Related Art
Ceramic substrates, such as low-temperature cofired ceramic (LTCC) substrates, often comprise a stack of ceramic material sheets and conductive layers, with each conductive layer positioned between two adjacent ceramic sheets. Typically, conductive traces or interconnects as well as passive electronic components, such as resistors, capacitors, and inductors, are formed on one or more conductive layers. Furthermore, vias, including thermal and stacked vias, may extend through the ceramic sheets to connect the conductive layers. The conductive layers and the vias are typically constructed from a thick film paste made from silver (Ag). While silver is less expensive to use and offers very good electrical performance, particularly in the radio frequency (RF) band, silver has significant drawbacks when used as the conductive layer on the upper surface of the ceramic substrate. For example, silver has inferior chemical properties which can lead to the formation of oxides on the conductive layer and inferior mechanical properties which can lead to migration that forms electrical-short causing whiskers.